Error 21 usually indicates a problem with the power going from the battery to the controller. On most ebikes by Rad Power Bikes and those with an LCD display, this error code will be indicated by "ERROR 21" appearing on the LCD screen. On the RadRunner, which comes with an LED display, the error code will be indicated by a flashing indicator light at Pedal Assistance Level "0".
Read through these instructions and contact Rad Power Bikes Product Support if you have questions. If you are not confident in your ability to successfully and safely perform all steps, we recommend having the work performed by a local, certified, and reputable bike mechanic.
1. Turn the bike OFF. Press the MODE button until the bike and LCD Display turn OFF. Use the battery key to unlock and remove the battery from the bike. Once the battery is removed, press and hold the MODE button on the LCD Display Remote until the LCD Display has remained off for a few seconds, to ensure the electrical system is fully off and safe for maintenance activities.
2. Inspect the Battery’s Connection Point. Inspect the connection point on the battery where it locks on to the bike frame. It should appear clean and dry; make note and take photos of any signs of moisture, debris, or damage.
3. Inspect the Battery Mounting Tray Connection Point. Inspect the connection point on the bike frame where the battery attaches to the bike, which should also appear clean and dry. Note and take photos of any moisture, debris, or damage.
4. Locate the Controller and Cable running from the Controller to the Battery. The controller is a relatively small, black, rectangular box, which, on most models, is mounted to the seat tube of the bike frame. Locate the wire that runs between the controller and the battery. On this cable, there is a bulge, which is the inline connector.
5. Unplug the Controller-Battery Cable Connector. Grab the two sides of the connection and carefully pull the connector directly apart without twisting. Pull from the connector and not directly on the cables.
6. Inspect the Controller-Battery Inline Connector. Check the inside of the inline connector on this wire is dry and clean and that the pins of the connector are properly aligned and undamaged. If moisture, debris, or damage is present, make note, take photos, and contact Rad Power Bikes Product Support. If the connections appear dry, clean, and undamaged, continue to the next step in this document.
7. Reconnect the Controller-Battery Connector. Align the two sides of the connector accurately and carefully press the two sides directly together without twisting, to fully reconnect them.
8. Next steps. Reinstall the battery and press and hold the MODE button on the LCD Display Remote to turn the display back on. If the error message persists, or the connection shows apparent damage, take photos of the damage, send them to Rad Power Bikes Product Support, and wait for next steps.
Phone: 1-800-939-0310 x 2